Balanced current-directional relay for the detection of multiphase line defects

ABSTRACT

A triphase line current-directional relay includes a reference impedance fed by symmetrical components of the currents, a reference voltage and a phase computer connected both to the reference impedance and to the reference voltage.

United States Patent Souillard BALANCED CURRENT-DIRECTIONAL RELAY FORTHE DETECTION OF MULTIPHASE LINE DEFECTS Inventor: Michel Henry PierreSouillard, Fontenayaux-Roses, France Assignee: Comnagnie Des Compteurs,Paris, France Filed: Aug. 10, 1970 Appl. No.: 62,400

Foreign Apbllcation Priority Data [4 1 Mar. 21, 1972 Dewey ..3l7/36 DPrimary ExaminerJames D. Trammell Attorney-Pierce, Scheffler & Parker57] I ABSTRACT Aug. 1 1, 1969 France ..692755l mphase linecunem'dmaicnonal relay mdudes a reference lmpedance fed by symmetrlcalcomponents of the currents, a reference voltage and a phase computerconnected both to the US. Cl ..3l7/27 R, 317/36 D, 324/86 referenceimpedance and to the reference voltage Int. Cl. ..H02h 3/26 Field ofSearch ..317/36 D, 27 R; 324/ 107, 86 4 Claims, 3 Drawing Figures c 324*l 0 i b x 1 C} e 51 I I n I z l/O Z R (o 6' 1 [O f D BALANCEDCURRENT-DIRECTIONAL RELAY FOR THE DETECTION OF MULTIPI-IASE LINE DEFECTSThe invention relates to a balanced relay of the type generally in useon a triphase leading out line or more generally at a contrast-block.

It is of common knowledge that a conventional homopolar or zero-sequencecurrent-directional relay is used to measure the relative displacementof homopolar values -voltage and currentat a leading out line terminal,in order to spot any ground defect upstream or downstream as comparedwith the junction point of the relay at a leading out line terminal,i.e., at the measurement point.

In the case of a high-voltage network including direct and multiplegroundings of transformer neutrals, the homopolar impedance on the barsets of the transformer blocks may be extremely low, while the homopolarimpedance of a long line has a high value as compared with the homopolarimpedance of the power supply units. As a result, the homopolar voltagemeasured at the leading out terminal may be extremely low in the case ofa remote ground defect occuring close to the other line terminal.

The responsiveness of a conventional homopolar currentdirectional relayis in such case far too low, and the steering thereofmay even be madeerroneous if the homopolar voltage is too low as compared with themismatching pseudohomopolar voltage inherent in the actual mismatchingwith respect to the ratio of negative boosters which have to be used onhigh voltage lines.

The object of this invention is to overcome the aforesaid inconveniencesby means of a triphase line current-directional relay wherein negativecurrent boosters set into the three phases respectively supply,according to a balanced connection, a reference impedance supplying aninitial reference voltage, proportional to a balanced component of thecurrent, negative voltage boosters set into the three respective phasessupply auxiliary transformers the corresponding secondary circuitsthereof connected in open triangle supply a second reference voltage,proportional to a voltage of the same balanced component of the current,a phase comparator being connected, on the one hand, to the terminals ofthe reference impedance, and, on the other hand, to the outputs of saidsecondary circuits, thereby allowing the phase comparator to send out alogic order the state thereof being dependent on the relative phasedisplacement between the first reference voltage and a voltage equal tothe sum of the first and the second reference voltages.

According to an embodiment of the invention, said negative currentboosters supply'the reference impedance through a homopolar connectionso that said first reference voltage is proportional to the homopolarcurrent, said auxiliary transformers supplying also a homopolar voltageserving as the second reference voltage.

According to another embodiment of the invention, the first and secondreference voltages are replaced by the inverse values of currents andvoltages deriving from reverse component filters and applied to thephase comparator.

Other features of the invention appear from the description whichfollows and from the accompanying drawings given as non-restrictiveembodiment examples.

FIG. 1 is a single-phase homopolar diagram equivalent to that ofa line.

FIG. 2 is a synoptic diagram of the relay arrangement constituting theobject of the invention.

FIG. 3 illustrates an embodiment of the preferred form of the relay.

Although the invention is also applicable to iriverse components, theinvention is described hereinafter according to a preferred embodimentwith reference to zero-sequence or homopolar components.

In the general case illustrated by FIG. 1, with respect for instance toa defect 1 situated downstream a measurement point A, the relationbetween zero-sequence or homopolar values may be written as follows:

V 20s wherefrom 20 Vo/Io Zas wherein:

Z0 is the reference homopolar impedance seen at the junction point ofthe relay at the leading out terminal of the line;

V0 is the reference homopolar voltage;

10 is the reference homopolar current;

20s is the source homopolar impedance upstream measurement point A. 1

In the case of a defect 2 situated upstream measurement point A, butdownstream a point B representing the remote end of line AB checked by aprotection device set at point A (a similar protection device is alsoset at point B), it applies that:

V0 (Zo Z'os) l wherefrom Z0 V0/I0 Z0, Zos wherein: Zos is the homopolarimpedance of the source situated downstream point B; and 20, thehomopolar impedance of line AB.

In order to allow the reading of said both defect cases, the homopolarcurrent-directional relay R (FIG. 2) includes a reference impedance Zsupplied by contingent defect current 10 through a transformer Tcsupplying a voltage 2, 10. Said impedance Z is a representation of apart of homopolar impedance Zo of the line and is chosen with a similarargument to those used for homopolar impedances of the network units.

The moduli of the homopolar impedances of the network, either upstreampoint A (20s), or downstream B (Z'os), have not practically to be known;however, they must have a noninfinite value to allow the existence ofhomopolar current 10 and make possible directional measurement. Besides,the directional measurement process according to the invention impliesthat the argument of homopolar impedances Zos and Z0: be set at aboutthe same value as that of homopolar impedance 20,, of the line. This isalways the case with a high voltage network wherein the neutrals thereofare directly grounded.

A transformer T, connected with the three conductors supplies referencevoltage V0 and a phase comparator unit C is supplied by referencevoltages (V0 Z I0) and (-Z 10).

The relative phase displacement of said two voltages is defined by theargument of the ratio of the complex expressions of said voltages, i.e.:

which features the relay according to the invention, gives:

Downstream defect case 1 Z 1 (4-) Upstream defect case 2 +l (5) In orderto simplify the equation, it will be assumed that alf impedances 2 havethe same argument which is a common case. The impedance quotient is thusa real number which is equal to the impedance modulus ratio. The phasecomparator unit C of the relay then takes into account the sign ofequations (4) and (5).

Thereby, in the case of any downstream defect l, the value Z as ispositive, even in the low source impedance ultimate case, i.e., in thecase where Zos tends to null.

In the case of any upstream defect 2, the value must be negative but notnull to allow distinctly the detection of any upstream defect. Thiscondition will be answered by choosing for reference impedance Z a valuebelow that of the homopolar impedance of line Z0, and this whatever thevalue of Zos may be. Practically, 2,, /6 20, will be chosen.

FIG. 3 illustrates in greater details an embodiment of relay R connectedwith leading out conductors a, b, c of a triphase network includingconductors A B C Transformer Tc forms negative current boosters TC TC TCwhich energize by means of a homopolar connection the primary Zr ofimpedance 2,, made of a mutual inductance; the secondary thereof Zr isshunted by a resistor r so as to set the argument of reference impedanceZ and to supply a reference voltage Z I0.

Negative voltage boosters Ta, Tb, Tc, connected with conductors a, b, cof the triphase leading out line, supply the respective primaries rd teIf, of three auxiliary transformers Td, Te, Tf forming the transformer Tshown on FIG. 2, the respective secondaries rd te tf thereof beingconnected in open triangle so as to supply a voltage V to the phasecomparator C.

A great number of different types of static or electromechanical phasecomparator relays are of common knowledge and, therefore, thedescription thereof is not essential for the understanding of theinvention. It is sufficient that the comparator chosen establish Fresnelvectors representing voltages V0 Z Io and 2, 10 which are in-step in thecase of a downstream defect and the same vectors in-opposition in thecase of an upstream defect.

Phase comparator C must therefore send s distinct signal D for the twoabove cases; the so-called inversion zone of such a comparator thuscorresponds to a square or 77/2 displacement of the above mentionedvectors.

By way of illustration, a phase comparator fitted with a ring codersupplying a galvanometric relay may be given as an example.

From reference voltages 2, 10 and V0, are obtained values (V0 Z I0) and(Z Io) which are applied as inputs to comparator C and which must answerthe two upstream or downstream defect cases defined in equations (4) and(5 Directional differentiation implies that the relative phase ofvoltages (V0 Z [0) and (Z IO) be reversed in the case ofa downstreamdefect with respect to the case of an upstream defect. Said condition isalways answered if the tuning condition Z Z0 mentioned above is actuallycarried out, since values defined in equations (4) and (5) have thenalways an opposite sign.

Output terminal D of phase comparator C sends a logic signal and thestate thereof depends on the relative displacement of lead-in or inputvoltages (V0 Z [0) and (-Z Said signal is used, for instance, for thecontrol of a circuit breaker S or a defect warning device.

In the foregoing, filters for voltage and current homopolar componentsare used, the filter of the homopolar components of the current giving10 value A (la lb 10) being the transformer Tc and the filter forvoltage homopolar components giving V0 value /6 (Va Vb Vc) being thetransformer T, shown on FIG. 2.

Instead of transformers Tc and T,, mentioned above, filters may be setwhich are respectively responsive to the respective inverse symmetricalcomponents of the currents and voltages in the various phase conductors.In this case, relay R operates according to the inverse values ofcurrent Ii and voltage Vi originated from the defect asymmetry, in thesame manner as with homopolar values. The diagram is identical to thatof FIG. 1 and, with respect to mathematic equations, the indices beingmerely changed. The formulae used for explaining the operation areidentical to those described above but transposed in inverse values. Toobtain a proper directional working, reference impedance Z must be lowerthan the inverse impedance of line Zi For the embodiment of the relay,phase comparator C must be supplied by the values originated fromfilters of voltage and current inverse components.

I claim: 1. A triphase line directional relay including negative currentboosters set into the three respective phases, a reference impedance fedaccording to a symmetrical connection from said phases and supplying afirst reference voltage proportional to a symmetrical component of thecurrents, negative voltage boosters set into the three respective phasesand feeding auxiliary transformers, the secondaries thereof beingconnected in open triangle, thereby supplying a second reference voltageproportional to the same symmetrical component, and a phase comparatorconnected with the reference impedance and the secondary of thetransformer, said phase comparator sending an output logic signal thestate thereof being dependent on the relative phase displacement betweenthe first reference voltage and a voltage equal to the sum of the firstand second reference voltages.

2. A relay according to claim 1 wherein the first and second referencevoltages are the homopolar components of the currents and voltagesoriginated from voltage and current homopolar filters.

3. A relay according to claim 1 wherein the first and second referencevoltages are the inverse values of currents and voltages originated frominverse component filters and are applied to the phase comparator.

4. A relay according to claim 1 wherein said negative current boosterssupply the reference impedance by means of a homopolar connection, sothat said first reference voltage is proportional to the homopolarcurrent, said auxiliary transformers supplying also a homopolar voltageas said second reference voltage.

1. A triphase line directional relay including negative current boostersset into the three respective phases, a reference impedance fedaccording to a symmetrical connection from said phases and supplying afirst reference voltage proportional to a symmetrical component of thecurrents, negative voltage boosters set into the three respective phasesand feeding auxiliary transformers, the secondaries thereof beingconnected in open triangle, thereby supplying a second reference voltageproportional to the same symmetrical component, and a phase comparatorconnected with the reference impedance and the secondary of thetransformer, said phase comparator sending an output logic signal thestate thereof being dependent on the relative phase displacement betweenthe first reference voltage and a voltage equal to the sum of the firstand second reference voltages.
 2. A relay according to claim 1 whereinthe first and second reference voltages are the homopolar components ofthe currents and voltages originated from voltage and current homopolarfilters.
 3. A relay according to claim 1 wherein the first and secondreference voltages are the inverse values of currents and voltagesoriginated from inverse component filters and are applied to the phasecomparator.
 4. A relay according to claim 1 wherein said negativecurrent boosters supply the reference impedance by means of a homopolarconnection, so that said first reference voltage is proportional to thehomopolar current, said auxiliary transformers supplying also ahomopolar voltage as said second reference voltage.